Attrition-mill



(No Model.) I T. L. STURTEVANT 8v M. G. DAVIS.

ATTRITION MILL.

No. 403,970. Patented May'28, 1889.

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UNITED STATES PATENT OFFICE.

THOMAS L. STURTEVANT, OF FRAMINGHAM, AND MILTON G. DAVIS, OF SOMERVILIIE, MASSACHUSETTS ATTRlTION-MILL.

SPECIFICATION forming part of Letters Patent No. 403,970, dated May 28, 1889.

Application filed July 30, 1886. Renewed July 23, 1888. Serial No. 280,796. (No model.)

To (all whom, it may concern.-

Be it known that we,THOMAs L. STU RTEVANT and MILTON G. DAVIS, citizens of the United States, residing, respectively, at l ramingham and Som erville, in the county of Middlesex an d State of Massachusetts, have invented certain new and useful Improvements in Attrition- M ills; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

This invention relates to that class of attrition or grinding mills in which two oppositely disposed heads axially aligned and containing the material to be pulverized are rotated in contrary directions, or in the same direction. Hitherto in this class of mills an exhaust device has generally been employed to create inward draft through the mill and carry oif some of the fine particles as they were reduced; but the current of air thus brought into the mill from the exterior served also to prevent in a greatmeasure, or entirely, the escape of fine particles outwardly from the mill.

The object of our invent-ion, which relates more especially to dry mills, so called, is to create and provide for the continuous free passage of air into and out of the mill at all times, and thus stop the escape of fine material which now occurs at certain intervals. A ditficulty heretofore has been the partial clogging of the screen-passages in the mill-casing, whereby the volume of air passing into the mill was checked and the fine material. emerged from between the rotary heads and mill-casing, or the removable ring arranged thereabout, which was secured to said millcasing. By the employment of an exterior-lydisposed air-conveyor, hereinafter more particularly described, a certain volume of air is continuously caused to flow into the mill and escape freely therefrom. Thus the necessary inward current is caused to be maintained, and in lieu of passing the air solely through the screening surface of the mill it is, after entering between the rotary heads and millcasin g, diverted therefrom and flu ally emerges below the screens. Presuming that clogging has occurred, the desired inward current by our device is effectively maintained, and no dust, or but little, ever escapes outwardly from the mill when employed.

The drawings accompanying this specification represent, in Figure 1, a longitudinal vertical section centrally of an attrition mill provided with our improvements, while Fig. 2 is a side view looking in direction of arrow 1 of the air-conveyor.

In the drawings only one side and a portion of the casing of an attrition-mill is represented, since the opposite side and the cor responding portion of the casin g are similarly constructed.

At A is shown a standard upon which is mounted a shaft, B, provided with a drivingpulley, C. At one extremity of this shaft is secured a rotary head, D, to which is affixed a hollow bushing, E, which enters and approximately fits the circular aperture in the air-conveyer II, which is secured in the opening F of the mill-casing G and bolted thereto. Then the mill is employed, the rotary heads are adjusted, as shown in Fig. 1, and project a short distance beyond and into the interior of the mill-casing.

Hitherto in dry mills packing devices of various kinds have been employed to prevent the escape of fine materiahwhich occurs about the rotary heads or between them and the mill-casing. In lieu of packing we have also employed an inward draft, but objections to its use have also occurred, since at times, when the free ,flow of air was prevented through the screens by partial clogging of the same, the draft was checked and the dust escaped, as before described, exteriorly of the mill. \Vc have overcome this dilficulty by doing away entirely with packing, which occasions much unnecessary friction, and by maintaining a continuous current inwardly about the rotary heads into and within the mill the escape of fine dust is prevented. To accomplish this latter result, in lieu of passingthe air through the mill solely by way of the screens with its attendant disadvantages, we cause the current of air to be at once diverted into a separate and less-obstructed passage about and around the mill whenever any serious obstruction or clogging of the screens occurs. This is accomplished by means of an air-conveyer, H, which is preferably a hollow ring provided with the air-passage a and with a projecting flange, by means of which it is firmly secured to the mill-casing, exteriorly of the latter, and partially inclosing the totary head. Entrance for the air into the mill is permitted by means of an annular passage, b, formed by making the interior periphery of the air-conveyer H, or that portion of said air-conveyer which is contiguous to the rotary head or bushing, slightly larger than the latter. Thus the induced air-supply is fur nished by means of this passage Z), and the air, rushing in, creates a sufficiently strong current and prevents escape of fine material so long as the screens, portions of which are shown at I I, remain open and permit free passage and flow of the air. In the event of said screens becoming clogged or partially obstructed by the fine material, some other escape for the volume of air requisite to form the desired current must be provided, in order to prevent the escape of fine particles outwardly. This is eltected by constructing in the material composing the air-conveyer H, upon the inner face of the latter, a circular duct, 0, preferably cone-shaped in crosssection, which is obliquely disposed in close proximity to the air-supply passage 1? and connects the interior of the mill with the passage a. Thus the air-current between the passage Z) and the ductcis but little obstructed by the agitated material in process of grinding; hence it will be readily understood that in the event of any obstruction in the screens the strength of the current required to prevent escape of fine particles will be maintained, for the air is at once diverted, and, although passing into the mill, will emerge and flow exteriorly about the latter of the mill below the screens I I. Therefore the dust will be prevented from accumulat- Thus the re- I ing and. obstructing the discharge or outlet passage J of the air-conveyer, and will readily be conveyed therefrom to its proper destination.

WVe claim- 1. In an attrition-mill, the combination, with the mill-casing and the rotary head, of an air-conveyer, as described, having the central opening, I), fitted directly to the grinding-chamber for external air-supply thereto, the circular lateral discharge-aperture 0, also connecting with said grindingchamber, and the tubular duct a,discharging by its port J within the mill-casing below the screen-bars, substantially as herein described. p

2. The rotary head D, the mill-casing G, provided with the aperture F, and the screens I I, combined with the annular air-conveyer H, having a central external aperture, 1'), fitted directly to the grinding-chamber, the interior circular duct, 0, leading from said chamber, the passage a, and outlet J, substantially as specified.

In testimony whereof we affix our signatures in presence of two witnesses.

THOMAS L. STURTEVANT.

MILTON G. DAVIS.

Witnesses:

H. E. LODGE,

F. CURTIS. 

